The present invention relates to the art of presses and, more particularly, to hydraulic fluid shock dampening systems and arrangements for a shearing press.
In a shearing press, as is well known, cooperable cutting die or shearing components are mounted on the press slide and bed to achieve cutting or shearing of material therebetween in response to movement of the press slide through the downward portion of its total stroke. Upon engagement of the die component on the slide with the material to be severed a load is placed on the press which progressively increases to a maximum which is reached at the point of breakthrough of the die components with respect to the material therebetween. This load is imposed on the press through the slide, and movement of the slide toward the press bed is restrained during the severing operation. This restraint is removed upon breakthrough, whereupon slide movement toward the press bed is accelerated as a result of the load build up. In the absence of a restraining force with respect to such accelerated movement of the slide, objectional shock loads and vibration forces are set up within the press. Such shock and vibration is detrimental to press life as well as maintenance expenses in connection with component parts of the press. Moreover, these shock and vibration forces result in objectionably high noise levels and impart undesirable vibration to other equipment and to the personnel working in the vicinity of the press. Moreover, it will be appreciated that these undesirable characteristics are repeated with each stroke of the press and are related in degree of objectionability to the size of the press.
Efforts have been made heretofore to dampen such shock and vibration forces experienced with the operation of a shearing press. While some success has been achieved in connection with reducing shock and vibration, the systems heretofore proposed for this purpose do not provide optimum efficiency with regard to vibration and noise abatement over a desirable period of continuous use of a given press. Additionally, systems heretofore proposed have characteristics which are detrimental to press life and economical press operation. With regard to such prior art efforts, it has been proposed, for example, to employ a hydraulic shock absorbing system including one or more piston and cylinder units interposed between the press bed and slide to define chambers receiving hydraulic fluid under pressure. During movement of the slide toward the bed to achieve a shearing operation fluid is expelled from the chamber or chambers through a variable restricted passageway incorporated in the piston component and adjusted to provide a predetermined restriction to flow from the chamber at the point of breakthrough of the material being severed. Such a system enables continuous, though restricted, movement of the slide following breakthrough and, thus, the imposition of some shock and vibration forces on the press. Moreover, if two or more such piston and cylinder units are employed in a given press, the adjustment thereof must be extremely accurate to avoid eccentric loading of the slide as a result of different pressure drops across the restrictions of the different units. Still further, the accuracies required in these units makes the system extremely expensive, and continuous operation of the press results in a requirement for frequent adjustment of the units whereby down time of the press is undesirably high as is maintenance time and expense. Additionally, continuous operation of the press with continuous flow of hydraulic fluid from the cylinder chambers each time the slide strokes results in undesirably high fluid temperatures which may necessitate the use of a cooling system therefor, thus adding to the cost of production and expensive operation of the press. Still further, even if just one piston and cylinder unit is employed to avoid the possibility of eccentric loading of the slide, the accuracy required with regard to adjusting the point of maximum restriction to coincide with the point of material breakthrough is impractical.
Other systems heretofore proposed have included a fixed orifice in the hydraulic system operable to pass hydraulic fluid from a fluid receiving chamber to a tank or the like by a low pressure drop during initial cutting of the material and at a high pressure drop when breakthrough occurs. The high pressure drop provides a restraining force against the slide. Systems of the latter character have poor efficiency with regard to reducing shock and noise and, additionally, generate excessive heat in the fluid due to the substantially continuous flow thereof under pressure.
With further regard to hydraulic shock dampening systems for shearing presses, the structural arrangements heretofore provided have been designed for a given press and, at least to some extent, have required certain component parts of the system to be a part of the physical structure of the press for which the system is designed. Still further, while such systems may include a piston and cylinder arrangement between the slide and bed of the press, the hydraulic circuitry associated therewith including, for example, high pressure responsive safety devices, flow control valves, hydraulic fluid accumulators and the like are mounted on or adjacent the press and thus are structurally separate from the piston and cylinder units and/or the mounting thereof on the press and are operatively associated therewith through long fluid flow lines therebetween. Such prior structural arrangements limit the capabilities of a given press from the standpoint of modification of the shock dampening system in accordance with work to be performed by the press. Additionally, such prior structural arrangements at least for practical purposes are not interchangeable such that at least a major portion of the system can be readily disassembled from one press and mounted on another, or such that tooling for a particular metal cutting operation and having a major portion of the shock dampening system components structurally associated therewith could be selectively employed with any one of a number of different presses.
In accordance with the present invention, the disadvantages of previous shock dampening systems provided in connection with shearing presses, including those specifically enumerated hereinabove, are minimized or overcome. In this respect, with regard to one aspect of the invention, maximum restraint of slide movement following breakthrough is achieved by quickly and positively blocking fluid flow from hydraulic fluid receiving chambers interposed between the press slide and bed. This maximum restraining force provides increased efficiency in reducing shock and noise by minimizing the load energy released and thus slide movement following breakthrough. Moreover, by positively blocking fluid flow from the chamber or chambers there is very little heat generated in the system fluid. Accordingly, the necessity of cooling systems are avoided as is the danger of excessive heat in the system without such a cooling system.
Preferably, such shutoff of fluid flow from a fluid chamber at the point of breakthrough is achieved by a flow sensitive valve in the fluid system which is responsive to acceleration of the slide at the point of breakthrough to block fluid flow from the chamber or chambers. Further, the shock and vibration loads imposed on the press by energy release at breakthrough can be further reduced by using a minimum volume of hydraulic fluid in the system, by using a fluid having a high bulk modulus, and and by rapid response of the flow sensitive valve. Preferably, the flow sensitive shutoff valve provides restricted flow from the chamber or chambers with minimal pressure drop during the cutting operation up to the point of breakthrough. At the point of breakthrough, acceleration of the slide positively shuts the valve producing a rapid counterload against slide movement, thus reducing the energy release experienced at breakthrough and maintaining the load on the press through the slide, thus to minimize shock, vibration and noise.
In accordance with another aspect of the invention, the hydraulic fluid receiving chambers of a shock dampening system are structurally incorporated in a bolster plate or a tooling assembly removably mountable on the press bed, thus enabling interchangeability thereof with a number of different presses and facilitating maintenance thereof without requiring shut down of the press for this purpose. Such a structural arrangement further facilitates designing a system for a given tooling assembly to provide a structural unit which can be readily assembled and disassembled for use with any one of a number of different presses. Preferably, components for controlling the flow of fluid from the hydraulic fluid receiving chamber such as the shutoff valve referred to hereinabove and fluid pressure responsive relief devices such as accumulators are structurally incorporated in the bolster plate or tooling assembly for mounting and removal from the press therewith. Fluid flow communication between the components of such a structural unit is provided in part by passageways provided in the bolster plate or components of the tooling assembly adapted to be connected to the source of hydraulic fluid under pressure. Accordingly, when the structural unit is mounted on the press bed it is only necessary to connect such a passageway or passageways with the hydraulic fluid source to prepare the shock dampening system for use. Likewise, when removal of the structural unit is desired, it is only necessary to disconnect the hydraulic fluid supply lines and then dismount the structural unit from the press bed. Accordingly, in addition to the interchangeability provided by such a structural unit, a minimum amount of time and effort is required to mount and dismount the unit with respect to a given press. Moreover, it will be appreciated that such a structural unit facilitates the performace of maintenance on the component parts thereof, and that the interchangeability provides economical advantages through use of a given unit with different presses.
It is accordingly an outstanding object of the present invention to provide an improved hydraulic shock dampening system for shearing presses.
Another object is the provision of a shock dampening system of the foregoing character which minimizes energy release, with respect to the load on the press, upon breakthrough of the material being severed.
Yet another object is the provision of a shock dampening system of the foregoing character which efficiently minimizes the imposition of shock and vibration forces on a press and the resultant noise level of the press during shearing operations.
Still a further object is the provision of a shock dampening system of the foregoing character which positively blocks fluid flow from an expansible chamber unit interposed between the press slide and bed at breakthrough of the material being severed, thus to minimize energy release with respect to the slide at the point of breakthrough and maximize slide restraining force.
Yet another object is the provision of a shock dampening system of the foregoing character in which a flow sensitive valve is employed to permit restricted flow of hydraulic fluid from the expansible chamber device during cutting of material up to the point of breakthrough and which is responsive to acceleration of the slide at the point of breakthrough to close the valve and thus block further fluid flow from the expansible chamber device.
Still another object is the provision of a shock dampening system of the foregoing character which is inexpensive to manufacture and install and which is highly efficient in operation throughout long periods of continuous use, thus minimizing down time of the press and maintenance time and expense.
A further object is the provision of a hydraulic shock dampening system for a shearing press in which component parts of the system are structurally interrelated as a unit enabling interchangeability thereof between presses.
A further object is the provision of a shock dampening system of the foregoing character in which at least a variable volume fluid receiving chamber and a component for controlling fluid flow therefrom are structurally incorporated either in a bolster plate or a tooling assembly removably mountable on a press bed.
Yet a further object is the provision of a shock dampening system of the foregoing character in which the major components of the system including fluid pressure responsive relief components are structurally associated with the bolster plate for removal therewith as a unit from the press bed to facilitate the performance of maintenance thereon as well as the interchangeability thereof between presses.
Another object is the provision of a shock dampening system of the foregoing character in which components of the system are structurally associated with a tooling arrangement for removal therewith as a unit from a given press, thus enabling the tooling arrangement and its associated shock dampening system components to be interchanged between presses.
Yet another object is the provision of a shock dampening system of the foregoing character in which a bolster plate or tooling components are structurally interrelated with components of the system to provide a structurally compact unit readily mountable and dismountable with respect to a press bed to facilitate maintenance and/or interchangeability and which, when mounted on a press bed, need only be connnected to a source of hydraulic fluid under pressure in preparation for use.